1. Field of the Invention
This invention relates to oil and gas well equipment and has particular reference to a sealing plug for a wellhead and method of making the same.
2. Description of the Prior Art
In the operation of an oil or gas well, an arrangement of valves, termed a Christmas Tree, is usually supported on the wellhead to facilitate remedial and maintenance work on the well. Such valve trees are expensive and complicated and they, themselves, must be serviced occasionally.
In my U.S. Pat. No. 4,804,045, issued on Feb. 14, 1989, I have disclosed and claimed a diversionary spool assembly which is intended to be incorporated in a wellhead and which enables the valve tree to be removed from the wellhead when the tree is not being used. Thus, a single valve tree can be used to service a number of wells, thus obviating the cost of providing a valve tree for each well. The diversionary spool assembly includes a head bore which is normally sealed by a removable plug to permit access through the bore to the interior of the well. Since relatively high pressures, sometimes in the order of 20,000 psi, are generally encountered in such well the plug must be securely sealed in the head bore and yet must be readily removable therefrom.
Accordingly, the plug must be firmly seated, preferably against a shoulder, in the bore. In most cases the plug is composed of two parts with a seal located between the two, in which case one part must be forced toward the other to expand the seal into intimate contact with the bore. In the seating and sealing of the plug, it is desirable that the plug and seal not rotate. Where a metal seal is used, rotation of the seal during expansion thereof into sealing condition can cause abrasion or scoring of both the seal and bore giving rise to the formation of minute scratches through which fluid can leak. Where pliable (plastic or composition) seals of the chevron type are used, rotation of the seal during expansion into sealing condition can damage the seal beyond its ability to effect proper sealing. Where plastic or rubber O-ring seals are used, considerable care must be exercised in inserting the plug into the bore since any rotation of the seal while compressed in sealing engagement with the inner surface of the bore can likewise cause considerable wear on, and damage to, the seal.
I obviated the above-noted problems in the diversionary spool assembly of my aforementioned patent by providing camming screws that are threaded through the wall of the wellhead. Such screws are thus accessible from the exterior of the wellhead to cam the plug against its seat and to cause expansion of the seal against the bore surface. Although such camming screws are fairly satisfactory, it is possible for fluid under high pressure to leak past the screw threads. Also, separate means must be provided to remove the plug from the well.